1. Technical Field
The embodiments herein relates to a method of producing hydroxyapatite nanoparticles with various structural and morphological properties in general and in particular, to a method to improve the bond strength of a new dental adhesive to dentin by including the hydroxyapatite nanorods as biocompatible fillers with high purity, high crystallinity, high aspect ratio and high colloidal stability.
2. Description of the Related Art
Hydroxyapatite (HAp) having a chemical formulae (Ca10(PO4)6(OH)2) is one of the most biocompatible materials because of its similarity to the main mineral component of the hard tissues of human body such as bone, dental enamel and dentin. Due to its biocompatibility, bioactivity, low solubility in water and ability to replace toxic ions in human body, HAp has widely been used in the biomedical applications. Since some applications of the HAp nanoparticles, for example, load-bearing orthopedic and dental applications are limited by the low mechanical properties of the HAp nanoparticles, numerous studies have been made to improve the mechanical properties using one-dimensional growth of the HAp crystals to form the nanorods.
Several methods such as solid-state synthesis, hydrothermal method and solvothermal method have been reported for the synthesis of hydroxyapatite nanorods. Although the preparation of the fibrous HAp particles is well known, the synthesis of nano-sized particles with high aspect ratio, appropriate stoichiometry and high crystallinity properties remains still as an interesting challenge.
Hydrothermal method is the most frequently used method for one-dimensional growth of HAp. However, the published data in the literature lead to some discrepancies on the optimum experimental conditions. For instance, some studies have shown that the fibrous HAp is synthesized at acidic or approximately at neutral conditions and some others show that these nanofibers are synthesized under alkaline conditions. Moreover, only few experimental parameters were evaluated in each study.
Dental adhesives, especially one step systems, are now widely used in restorative and artistic dentistry due to their conservative and generally aesthetic roles. In fact, the clinical performance of composite restorations partially depends upon the complete adhesion of the restorative composites to enamel and dentin. For enamel, the acid-etch procedure is performed usually and successfully. Dentin, however, is a hydrated biological composite, including inorganic materials (mostly hydroxyapatite), organic materials (collagen) and water, with properties that vary significantly with location. Moreover, the dentin contains fluid-containing dentinal tubules which make a dynamic and wet substrate for the bonding agents and a more complicated condition in comparison to the enamel.
Recently nanoparticles have been used in the formulation of the restorative composite systems. With the aim of improving physical and mechanical properties, nanoparticles have also been included into the dental adhesives. The filler particles are used in the dental adhesives to fortify the bond strength of the adhesive to the dentin by penetrating into the dentin tubules, decreasing the polymerization shrinkage and increasing the elastic modulus of the adhesive layer. Because of their very small sizes, nanoparticles are able to penetrate well into the dentinal tubules along with the adhesive matrix resin thereby providing a composite adhesive layer with improved properties.
Although the researchers have studied the effect of various functional or nonfunctional micro and nano-fillers on the dental adhesives for several years, the type and concentration of these fillers still remains a matter of concern. For example, the U.S. Pat. No. 6,620,861 B1 issued in 2003, disclosed the production of various organic and inorganic fillers for using in a dental composition. However, many of the prepared filler dental adhesives are very much process sensitive, show limited colloidal stability (for using in dental adhesives) due to the dilute characteristic of the adhesives and may increase the toxicological risk of the adhesive.
As the major component of an inorganic material of a tooth is hydroxyapatite, it might be a promising material for the preparation of new dental adhesives with improved mechanical and biological properties. Although HAp nanoparticles are currently used as coatings in orthopedic and dental implants, no information is available on the effect of hydroxyapatite on dentin-bonding systems.
Several patents such as U.S. Pat. No. 4,046,858 issued in 1997, disclosed the synthetic route to produce the crystalline HAp for production of various implants such as dental composition. However, the patents do not reveal the properties of such dental composition. Moreover, it has also been reported (in an article entitled Hydrolytic stability of experimental hydroxyapatite-filled dental composite materials by Domingo C et al., and published in Dent. Mater, 2003 19(6):478-486.) that a composite material containing a surface modified nanoparticle of hydroxyapatite is unsuitable for clinical performance.
The above mentioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification.